Finding and using sparse matrix indices

19 views (last 30 days)
I have the sparse matrix array L=
(36,67) 1
(39,70) 1
(42,73) 1
(45,76) 1
(48,79) 1
(51,82) 1
(54,85) 1
and a large matrix M. I need to use the index coordinates of each of the elements in L, offset the coordinates by some amount, find the element in matrix M having those coordinates, and multiply the result. The operation must be vectorized.
A pseudocode might look like:
out=L*M(Lrow+5,Lrow+Lcolumn-15);
where Lrow is the row in L and parentheses are the matrix coordinates in M, determined for each element in L.
Thanks.

Accepted Answer

Iain
Iain on 24 Feb 2014
If L is the same size as M:
idx = find(L);
Move the idx around by adding 1 (moves it down one), or by adding the number of columns (moves it right one) - Just be aware that if you move them down far enough, they'll move right.
idx = idx + 1 + cols; % right AND down one.
the_values = M(idx);

More Answers (0)

Categories

Find more on Sparse Matrices in Help Center and File Exchange

Products

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!